U.S. patent number 10,000,118 [Application Number 15/302,879] was granted by the patent office on 2018-06-19 for clutch control device for four-wheel-drive vehicle.
This patent grant is currently assigned to Nissan Motor Co., Ltd.. The grantee listed for this patent is Nissan Motor Co., Ltd.. Invention is credited to Shunichi Mitsuishi, Atsuhiro Mori, Makoto Morita, Katsuyoshi Ogawa, Tetsu Takaishi.
United States Patent |
10,000,118 |
Ogawa , et al. |
June 19, 2018 |
Clutch control device for four-wheel-drive vehicle
Abstract
A vehicle clutch control device is provided for switching from a
two-wheel drive traveling to a four-wheel drive traveling. The
vehicle clutch control device includes a dog clutch that separates
a rear wheel drive from a front wheel drive by releasing the dog
clutch, an electronically controlled coupling that distributes a
driving force of a transverse engine to left and right rear wheels
in accordance with a clutch connection capacity, and a four-wheel
drive control unit. The four-wheel drive control unit switches the
drive mode to one of a disconnect two-wheel drive mode in which the
dog clutch and the electronically controlled coupling are released,
a connect four-wheel drive mode in which the dog clutch and the
electronically controlled coupling are engaged, and a stand-by
two-wheel drive mode in which the dog clutch is engaged while the
electronically controlled coupling is released.
Inventors: |
Ogawa; Katsuyoshi (Kanagawa,
JP), Mori; Atsuhiro (Kanagawa, JP),
Mitsuishi; Shunichi (Kanagawa, JP), Morita;
Makoto (Kanagawa, JP), Takaishi; Tetsu (Kanagawa,
JP) |
Applicant: |
Name |
City |
State |
Country |
Type |
Nissan Motor Co., Ltd. |
Yokohama-shi, Kanagawa |
N/A |
JP |
|
|
Assignee: |
Nissan Motor Co., Ltd.
(Yokohama, JP)
|
Family
ID: |
54287738 |
Appl.
No.: |
15/302,879 |
Filed: |
March 30, 2015 |
PCT
Filed: |
March 30, 2015 |
PCT No.: |
PCT/JP2015/059976 |
371(c)(1),(2),(4) Date: |
October 07, 2016 |
PCT
Pub. No.: |
WO2015/156161 |
PCT
Pub. Date: |
October 15, 2015 |
Prior Publication Data
|
|
|
|
Document
Identifier |
Publication Date |
|
US 20170028843 A1 |
Feb 2, 2017 |
|
Foreign Application Priority Data
|
|
|
|
|
Apr 11, 2014 [JP] |
|
|
2014-082036 |
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
F16D
13/74 (20130101); B60K 17/35 (20130101); F16D
11/00 (20130101); F16D 25/0638 (20130101); B60K
23/08 (20130101); B60K 17/02 (20130101); F16D
21/00 (20130101); B60K 17/344 (20130101); F16D
48/06 (20130101); F16D 2500/3144 (20130101); B60Y
2300/427 (20130101); F16D 2500/3108 (20130101); B60Y
2400/4244 (20130101); B60Y 2300/52 (20130101); B60Y
2400/421 (20130101); F16D 2500/3115 (20130101); F16D
2500/31426 (20130101); B60Y 2400/424 (20130101); B60K
2023/0858 (20130101); F16D 2500/30806 (20130101); F16D
2500/10431 (20130101); B60K 17/3515 (20130101); B60K
23/0808 (20130101) |
Current International
Class: |
B60K
17/02 (20060101); F16D 13/74 (20060101); B60K
17/344 (20060101); B60K 23/08 (20060101); F16D
11/00 (20060101); F16D 25/0638 (20060101); F16D
21/00 (20060101); F16D 48/06 (20060101); B60K
17/35 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
62-178436 |
|
Aug 1987 |
|
JP |
|
2010-96254 |
|
Apr 2010 |
|
JP |
|
2010-254058 |
|
Nov 2010 |
|
JP |
|
2012-61923 |
|
Mar 2012 |
|
JP |
|
Primary Examiner: Burgess; Ramya P
Assistant Examiner: Morris; David R
Attorney, Agent or Firm: Global IP Counselors, LLP
Claims
The invention claimed is:
1. A vehicle clutch control device for a four-wheel drive vehicle
having a pair of main drive wheels connected to a driving source
and a pair of auxiliary drive wheels selectively connected to the
driving source, the clutch control device comprising: a drive mode
switching unit configured to perform a switching control of a drive
mode of the vehicle based on a vehicle state; a dog clutch
operatively disposed in a transmission path between the main drive
wheels and the auxiliary drive wheels to separate a system for
transmitting drive force to the auxiliary drive wheels from a
system for transmitting drive force to the main drive wheels by
releasing the dog clutch; and a friction clutch operatively
disposed in the transmission path between the main drive wheels and
the auxiliary drive wheels to allocate a portion of the drive force
from the driving source to the auxiliary drive wheels in accordance
with a clutch engagement capacity of the friction clutch, the drive
mode switching unit being configured to switch the drive mode of
the vehicle between a disconnect two-wheel drive mode, a connect
four-wheel drive mode and a stand-by two wheel drive mode, the dog
clutch and the friction clutch being released in the disconnect
two-wheel drive mode, the dog clutch and the friction clutch being
engaged in the connect four-wheel drive mode, the dog clutch being
engaged and the friction clutch being released in the stand-by two
wheel drive mode, the drive mode switching unit being further
configured to switch to the stand-by two-wheel drive mode and to
the connect four-wheel drive mode with less delay than switching to
the disconnect two-wheel drive mode.
2. The vehicle clutch control device according to claim 1, wherein
the drive mode switching unit is configured to bring the friction
clutch in a completely released state in the stand-by two-wheel
drive mode to enhance fuel efficiency, and the drive mode switching
unit is further configured to bring the friction clutch in a
released state immediately before connection to enhance four-wheel
drive performance while in the stand-by two-wheel drive mode.
3. The vehicle clutch control device according to claim 2, wherein
the drive mode switching unit is further configured to switch the
drive mode of the vehicle to the disconnect two-wheel drive mode in
a condition during which a vehicle speed is higher than a
predetermined threshold vehicle speed and a required driving force
is lower than a predetermined threshold driving force, the drive
mode switching unit is further configured to switch the drive mode
of the vehicle to the stand-by two-wheel drive mode in a condition
during which the vehicle speed is higher than the predetermined
threshold vehicle speed and the required driving force is higher
than the predetermined threshold driving force, and the drive mode
switching unit being is configured to switch the drive mode of the
vehicle to the connect four-wheel drive mode in a condition in
which the vehicle speed is lower than the predetermined threshold
vehicle speed.
4. The vehicle clutch control device according to claim 3, wherein
the predetermined threshold vehicle speed increases as the required
driving force increases.
5. The vehicle clutch control device according to claim 2, wherein
the drive mode switching unit is further configured to give
priority to a switching transition speed for switching to the
stand-by two-wheel drive mode and a switching transition speed for
switching to the connect four-wheel drive mode over a switching
transition speed for switching to the disconnect two-wheel drive
mode.
6. The vehicle clutch control device according to claim 2, wherein
the dog clutch is disposed upstream of a transfer mechanism
provided in a drive branch to the auxiliary drive wheels, and the
friction clutch is in a drive shaft leading to the auxiliary drive
wheel from the transfer mechanism that is connected to a propeller
shaft and a differential.
7. The vehicle clutch control device according to claim 2, wherein
the friction clutch is disposed upstream of a transfer mechanism
provided at a drive branch leading to the auxiliary drive wheels,
and the dog clutch is disposed in a drive shaft leading to the
auxiliary drive wheel from the transfer mechanism that is connected
to a propeller shaft and a differential.
8. The vehicle clutch control device according to claim 1, wherein
the dog clutch is disposed upstream of a transfer mechanism that is
provided in a drive branch to the auxiliary drive wheels, and the
friction clutch is in a drive shaft leading to the auxiliary drive
wheel from the transfer mechanism that is connected to a propeller
shaft and a differential.
9. The vehicle clutch control device according to claim 1, wherein
the friction clutch is disposed upstream of a transfer mechanism
provided at a drive branch leading to the auxiliary drive wheels,
and the dog clutch is disposed in a drive shaft leading to the
auxiliary drive wheel from the transfer mechanism that is connected
to a propeller shaft and a differential.
10. A vehicle clutch control device for a four-wheel drive vehicle
having a pair of main drive wheels connected to a driving source
and a pair of-auxiliary drive wheels selectively connected to the
driving source, the clutch control device comprising: a drive mode
switching unit configured to perform a switching control of a drive
mode of the vehicle based on a vehicle state; a dog clutch
operatively disposed in a transmission path between the main drive
wheels and the auxiliary drive wheels to separate a system for
transmitting drive force to the auxiliary drive wheels from a
system for transmitting drive force to the main drive wheels by
releasing the dog clutch; and a friction clutch operatively
disposed in the transmission path between the main drive wheels and
the auxiliary drive wheels to allocate a portion of the drive force
from the driving source to the auxiliary drive wheels in accordance
with a clutch engagement capacity of the friction clutch, the
friction clutch being housed in a clutch case having a clutch
chamber and an oil chamber, the clutch chamber containing the
friction clutch, the oil chamber being separated from the clutch
chamber by a partition wall, the clutch case further including an
oil passage through which lubricating oil from the clutch chamber
flows into the oil chamber due to a centrifugal force generated in
response to rotation of the friction clutch and by operation of an
on-off valve disposed in the partition wall, the drive mode
switching unit being configured to switch the drive mode of the
vehicle between a disconnect two-wheel drive mode, a connect
four-wheel drive mode and a stand-by two wheel drive mode, the dog
clutch and the friction clutch being released in the disconnect
two-wheel drive mode, the dog clutch and the friction clutch being
engaged in the connect four-wheel drive mode, the dog clutch being
engaged and the friction clutch being released in the stand-by two
wheel drive mode, the drive mode switching unit is configured to
bring the friction clutch in a completely released state in the
stand-by two-wheel drive mode to enhance fuel efficiency, and the
drive mode switching unit is further configured to bring the
friction clutch in a released state immediately before connection
to enhance four-wheel drive performance while in the stand-by
two-wheel drive mode, the drive mode switching unit being further
configured to close the on-off valve so that lubricating oil is
stored in the oil chamber to enhance fuel efficiency in the
stand-by two-wheel drive mode, and the drive mode switching unit
being further configured to open the on-off valve so that
lubricating oil flows from the oil chamber into the clutch chamber
to enhance four-wheel drive performance in the stand-by two-wheel
drive mode.
11. The vehicle clutch control device according to claim 10,
wherein the drive mode switching unit is further configured to
switch the drive mode of the vehicle to the disconnect two-wheel
drive mode in a condition during which a vehicle speed is higher
than a predetermined threshold vehicle speed and a required driving
force is lower than a predetermined threshold driving force, the
drive mode switching unit is further configured to switch the drive
mode of the vehicle to the stand-by two-wheel drive mode in a
condition during which the vehicle speed is higher than the
predetermined threshold vehicle speed and the required driving
force is higher than the predetermined threshold driving force, and
the drive mode switching unit is further configured to switch the
drive mode of the vehicle to the connect four-wheel drive mode in a
condition in which the vehicle speed is lower than the
predetermined threshold vehicle speed.
12. The vehicle clutch control device according to claim 10,
wherein the drive mode switching unit is further configured to give
priority to a switching transition speed for switching to the
stand-by two-wheel drive mode and a switching transition speed for
switching to the connect four-wheel drive mode over a switching
transition speed for switching to the disconnect two-wheel drive
mode.
13. The vehicle clutch control device according to claim 10,
wherein the dog clutch is disposed upstream of a transfer mechanism
provided in a drive branch to the auxiliary drive wheels, and the
friction clutch is in a drive shaft leading to the auxiliary drive
wheel from the transfer mechanism that is connected to a propeller
shaft and a differential.
14. The vehicle clutch control device according to claim 10,
wherein the friction clutch is disposed upstream of a transfer
mechanism provided at a drive branch leading to the auxiliary drive
wheels, and the dog clutch is disposed in a drive shaft leading to
the auxiliary drive wheel from the transfer mechanism that is
connected to a propeller shaft and a differential.
15. A vehicle clutch control device for a four-wheel drive vehicle
having a pair of main drive wheels connected to a driving source
and a pair of-auxiliary drive wheels selectively connected to the
driving source, the clutch control device comprising: a drive mode
switching unit configured to perform a switching control of a drive
mode of the vehicle based on a vehicle state; a dog clutch
operatively disposed in a transmission path between the main drive
wheels and the auxiliary drive wheels to separate a system for
transmitting drive force to the auxiliary drive wheels from a
system for transmitting drive force to the main drive wheels by
releasing the dog clutch; and a friction clutch operatively
disposed in the transmission path between the main drive wheels and
the auxiliary drive wheels to allocate a portion of the drive force
from the driving source to the auxiliary drive wheels in accordance
with a clutch engagement capacity of the friction clutch, the drive
mode switching unit being configured to switch the drive mode of
the vehicle between a disconnect two-wheel drive mode, a connect
four-wheel drive mode and a stand-by two wheel drive mode, the dog
clutch and the friction clutch being released in the disconnect
two-wheel drive mode, the dog clutch and the friction clutch being
engaged in the connect four-wheel drive mode, the dog clutch being
engaged and the friction clutch being released in the stand-by two
wheel drive mode, the drive mode switching unit being further
configured to switch the drive mode of the vehicle to the
disconnect two-wheel drive mode in a condition during which a
vehicle speed is higher than a predetermined threshold vehicle
speed that is greater than zero and a required driving force is
lower than a predetermined threshold driving force, the drive mode
switching unit is further configured to switch the drive mode of
the vehicle to the stand-by two-wheel drive mode in a condition
during which the vehicle speed is higher than the predetermined
threshold vehicle speed and the required driving force is higher
than the predetermined threshold driving force, and the drive mode
switching unit is further configured to switch the drive mode of
the vehicle to the connect four-wheel drive mode in a condition in
which the vehicle speed is lower than the predetermined threshold
vehicle speed.
16. The vehicle clutch control device according claim 15, wherein
the predetermined threshold vehicle speed increases as the required
driving force increases.
17. The vehicle clutch control device according to claim 15,
wherein the drive mode switching unit is further configured to give
priority to a switching transition speed for switching to the
stand-by two-wheel drive mode and a switching transition speed for
switching to the connect four-wheel drive mode over a switching
transition speed for switching to the disconnect two-wheel drive
mode.
18. The vehicle clutch control device according to claim 15,
wherein the dog clutch is disposed upstream of a transfer mechanism
provided in a drive branch to the auxiliary drive wheels, and the
friction clutch is in a drive shaft leading to the auxiliary drive
wheel from the transfer mechanism that is connected to a propeller
shaft and a differential.
19. The vehicle clutch control device according to claim 15,
wherein the friction clutch is disposed upstream of a transfer
mechanism provided at a drive branch leading to the auxiliary drive
wheels, and the dog clutch is disposed in a drive shaft leading to
the auxiliary drive wheel from the transfer mechanism that is
connected to a propeller shaft and a differential.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a U.S. National stage application of
International Application No. PCT/JP2015/059976, filed Mar. 30,
2015, which claims priority to JP Patent Application No.
2014-082036 filed on Apr. 11 2014, the contents of which are hereby
incorporated herein by reference.
BACKGROUND
Field of the Invention
The present invention generally relates to a clutch control device
for a four-wheel drive vehicle equipped with a meshing clutch and a
friction clutch in a driving force transmission system to an
auxiliary drive wheel.
Background Information
Conventionally, a four-wheel drive vehicle of a front wheel drive
base is known which is provided with a positive or meshing clutch
and a friction clutch in a driving force transmission system (for
example, refer to Japanese Laid Open Patent Application No.
2010-254058). In this four-wheel drive vehicle, the meshing clutch
and the friction clutch are connected at the time of the 4-wheel
drive, while the meshing clutch and the friction clutch are
released at the time of the 2-wheel drive. Further, at the time of
switching from a 2-wheel drive traveling to a four-wheel drive
traveling, after the friction clutch is connected, the meshing
clutch will be connected.
SUMMARY
In the conventional system, when switching from the 2-wheel drive
traveling to four-wheel drive traveling, the meshing clutch is held
with a rotational difference in a meshing Stand-by state until the
rotational difference disappears. Upon disappearance of the
rotational difference, meshing members are pushed together for
connection. Therefore, since switching from 2-wheel drive to the
four-wheel drive traveling requires a meshing latency or delay, it
is difficult to switch the traveling state promptly.
The present invention has been made in view of the above problems,
and aims to provide a clutch control device for a four-wheel drive
vehicle in which switching from 2-wheel drive to four-wheel drive
can be performed promptly.
In order to achieve the above object, a clutch control device for a
four-wheel drive vehicle according to the present invention
includes a drive mode switching unit which is mounted on a four
wheel drive vehicle in which, one of left and right front wheels
and left and right rear wheels are set as main drive wheels that
are connected to a driving source, while the others are set as
auxiliary drive wheels that are connected to the driving source via
a clutch. The drive mode switching unit is configured to perform
selective control of connecting/releasing of the clutch as well as
a switching control of a drive mode of the four-wheel drive vehicle
in accordance with a vehicle state. Further, the clutch includes a
meshing clutch and a friction clutch, in the driving force
transmission system to the auxiliary drive wheels, disposed
separately from each other and respectively arranged in a
transmission path, with respect to a differential interposed, on a
drive branch side on the one hand and in a transmission path of the
auxiliary drive wheels on the other. Here, the meshing clutch is
operable by releasing the meshing clutch to separate the driving
force transmission system to the auxiliary drive wheels from the
driving force transmission system to the main drive wheels. The
friction clutch may allocate or distribute part of the driving
force from the driving source to the auxiliary drive wheels in
accordance with the clutch connecting capacity. In addition, the
drive mode switching unit switches in one of modes, i.e., a
disconnect two-wheel drive mode with the meshing clutch and the
friction clutch released, a connect four-wheel drive mode with the
meshing clutch and the friction clutch connected, and a stand-by
two-wheel drive mode with the meshing clutch connected while the
friction clutch released.
Therefore, in the clutch control device for a four-wheel drive
vehicle according to the present invention, the drive mode of the
four-wheel drive vehicle is switched by the drive mode switching
unit in one of the disconnect two-wheel drive mode, the connect
four-wheel drive mode, and the stand-by two-wheel drive mode. Here,
when switching from the stand-by two-wheel drive mode to the
connect four-wheel drive mode, since the meshing clutch is already
connected, there is no need to newly connect the meshing clutch at
mode switching. In other words, when only the friction clutch is
connected, the two-wheel drive traveling may be switched to the
four-wheel drive traveling. Thus, the meshing waiting time for
meshing the clutch can be eliminated. Therefore, it is possible to
switch from the two-wheel drive traveling to the four-wheel drive
traveling as soon as possible.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a schematic diagram of a driving system of a four-wheel
drive vehicle of a front wheel drive base to which a clutch control
device is applied in accordance with a first embodiment;
FIG. 2 is a schematic diagram of a control system of a four-wheel
drive vehicle of a front wheel drive base to which the clutch
control device of the first embodiment is applied;
FIG. 3 is a base map illustrating a drive mode switching map based
on a vehicle speed and an accelerator position opening amount at
the time of selection of "auto mode" in the first embodiment;
FIG. 4 is a drive mode transition diagram illustrating the
switching transition of the drive modes (disconnect two-wheel drive
mode, standby two-wheel drive mode, and connect four-wheel drive
mode) at the time of selection of "auto mode" in the first
embodiment;
FIG. 5 is a flowchart illustrating a flow of a drive mode switching
process executed by the 4WD control unit in the first
embodiment;
FIG. 6 is a flowchart illustrating a flow of the disconnect the
two-wheel drive mode process executed by the 4WD control unit in
the first embodiment;
FIG. 7 is a flowchart illustrating a flow of the standby two-wheel
drive mode process executed by the 4WD control unit in the first
embodiment;
FIG. 8 is a flowchart illustrating a flow of the connect four-wheel
drive mode process executed by the 4WD control unit in the first
embodiment;
FIG. 9 is an explanatory diagram illustrating the movement of the
operating point on a drive mode switching map in the four-wheel
drive vehicle in the first embodiment; and
FIG. 10 is a driving system configuration diagram illustrating a
driving system configuration of a four-wheel drive vehicle with a
rear-wheel drive base to which a clutch control device is applied
in accordance with a second illustrated embodiment.
DETAILED DESCRIPTION OF THE EMBODIMENTS
Below, a description is given of the embodiments of the clutch
control device for a four-wheel drive vehicle according to the
present invention with reference to the first embodiment and the
second embodiment shown in the drawings.
First Embodiment
The clutch control device for a four-wheel drive vehicle of a front
wheel drive base (an example of a four-wheel drive vehicle) in
accordance with a first embodiment will be described separately in
the following sections--"drive system for a four-wheel drive
vehicle", "control system for a four-wheel drive vehicle", "drive
mode switching", and "drive mode switching process".
Drive System for a Four-Wheel Drive Vehicle
FIG. 1 schematically illustrates a drive system for a front wheel
drive-based four-wheel drive vehicle to which a clutch control
device is applied. Below, with reference to FIG. 1, description is
given of the drive system configuration of a four-wheel drive
vehicle.
The front wheel drive system for the four-wheel drive vehicle
includes, as shown in FIG. 1, a transverse engine 1 (driving
source), a transmission 2, a front differential 3, a left front
wheel drive shaft 4, a right front wheel drive shaft 5, a left
front wheel 6 (main drive wheel), and a right front wheel 7 (main
drive wheel). In other words, the driving force passing through the
engine 1 and the transmission 2 is transmitted to the left and
right front wheel drive shafts 4 and 5 through the front
differential 3 to drive the left and right front wheels 6 and 7 at
all times while allowing a rotational difference.
The rear wheel drive system of the four-wheel drive vehicle
includes, as shown in FIG. 1, a dog clutch 8 (meshing or claw
clutch), a bevel gear 9, an output pinion 10, a rear wheel output
shaft 11, a propeller shaft 12, a drive pinion 13, a ring gear 14,
a rear differential 15, an electronically controlled coupling 16
(friction clutch), a left rear wheel drive shaft 17, a right rear
wheel drive shaft 18, a left rear wheel 19 (auxiliary drive wheel),
and a right rear wheel 20 (auxiliary drive wheel). Note that a
universal joint is denoted by reference numeral 21. That is, in the
rear wheel drive system of the four-wheel drive vehicle, by
performing the connecting/releasing control of the dog clutch 8 and
the electronically controlled coupling 16, such a driving system
configuration is available in which the two-wheel drive traveling
with both the dog clutch 9 and the electronically controlled
coupling 16 released to thereby separate the left and right rear
wheels 19 and 20 as auxiliary drive wheels from the transverse
engine 1 (=disconnect two-wheel drive mode), and a four-wheel drive
traveling with both the dog clutch 8 and the electronically
controlled coupling 16 connected to thereby connect the left and
right rear wheels 19 and 20 as auxiliary drive wheels to the
transverse engine 1 (=connect four-wheel drive mode) is selectable.
Note that, by releasing the dog clutch 8, it is possible to stop
the rotation of the drive system on the downstream side of the dog
clutch (rotation of propeller shaft 12 and the like). Thus,
friction loss, oil agitation loss and the like may be suppressed,
and an improved fuel efficiency is achieved.
The dog clutch 8 is provided in the drive branch or bifurcation
position from the left and right front wheels 6 and 7 to the left
and right rear wheels 19 and 20, and is intended to cut off the
driving force transmission system to the left and right rear wheels
19 and 20 from the driving force transmission system of the left
and right front wheels 6 and 7 in response to release of the
clutch. An input-side meshing member (not shown) of the dog clutch
8 is connected to a differential case of the front differential 3,
and an output-side meshing member (not shown) of the dog clutch 8
is connected to a bevel gear 9. The dog clutch 8, the bevel gear 9,
the output pinion 10, and part of the rear wheel output shaft 11
are accommodated in a transfer case 23 fixed to the adjacent, front
differential housing 22. As the dog clutch 8, for example, such a
configuration is used in which one of a pair of meshing members is
installed as a fixed member while the other is set as a movable
member with a spring (not shown) disposed between the fixed member
and the movable member and biased in the connecting direction, and
a screw groove (not shown) is formed in the outer periphery of the
moving member so that a solenoid pin (not shown) can be fitted.
When the solenoid pin is projected with respect to the screw groove
and fitted, the moving member strokes in the releasing direction
while rotating, and releases the meshing connection in response to
the stroke amount exceeding a predetermined value. On the other
hand, when fitting of the solenoid pin to the screw groove is
released, the movable member strokes in the connecting direction
toward the fixed member by the spring bias and the teeth of the two
members interlock for connection.
The electronically controlled coupling 16 is disposed downstream of
the dog clutch 8, and serves to allocate part of the driving force
from the transverse engine 1 to the left and right rear wheels 19
and 20 in accordance with the clutch torque or connecting capacity.
An input side clutch plate 16a of the electronically controlled
coupling 16 is connected to the left side gear of the rear
differential 15 through a clutch input shaft 16b. An output side
clutch plate 16c of the electronically controlled coupling 16 is
connected to the left rear wheel drive shaft 17 through a clutch
output shaft 16d. The electronically controlled coupling 16 is
housed in a coupling case 25 (clutch case) fixed to a rear
differential housing 24 located in the adjacent position. As the
electronically controlled coupling 16, for example, such a
configuration may be used in having a multi-plate friction clutch
with a plurality of input-side clutch plates 16a and a plurality of
output side clutch plates 16c arranged alternately, a fixed cam
piston (not shown) and a movable cam piston (not shown), each
formed with a cam surface opposite to each other, and a cam member
that is interposed between the opposing cam surfaces. Meshing of
the electronically controlled coupling 16 is carried out by a cam
action to expand a piston gap which is generated by allowing an
electric motor (not shown) to rotate the movable cam piston,
movable cam piston stroke in the clutch meshing direction according
to the rotation angle, so that the movable cam piston strokes in
the clutch connecting direction in accordance with its rotation
angle to thereby increase a frictional connecting force of the
multi-plate friction clutch. Release of the electronically
controlled coupling 16 is carried out by another cam action to
narrow the piston gap which is generated by allowing the electric
motor to rotate in a direction opposite to the connecting
direction, so that the movable cam piston strokes in the clutch
releasing direction in accordance with its rotation angle to
thereby reduce the frictional connecting force of the multi-plate
friction clutch.
The coupling case 25, as shown enlarged in FIG. 1, is formed
therein with a clutch chamber 25b and the oil chamber 25c separated
from each other by a partition wall 25a. Further, the partition
wall 25a is formed with a flow port 25e which can be opened and
closed by an on-off valve 25d for enabling circulation of
lubricating oil encapsulated in the coupling casing 25. In
addition, the clutch chamber 25b and the oil chamber 25c are
communicated by an oil passage 25f.
The clutch chamber 25b provides an area for accommodating the
electronically controlled coupling 16 in the coupling case 25. The
oil chamber 25c provides an area in which the lubricating oil is
stored in the coupling case 25, that has moved from the clutch
chamber 25b via the oil passage 25f due to the centrifugal force
generated by rotation of the electronically controlled coupling
16.
The flow port 25e is a through hole formed in the partition wall
25a, and communicates the clutch chamber 25b and the oil chamber
25c. The on-off valve 25d is configured to open and close the flow
port 25e in conjunction with releasing/connecting operation of the
electronically controlled coupling 16. That is, the on-off valve
25d is enabled in conjunction with the movable cam piston. When the
movable cam piston strokes in the clutch releasing direction, the
flow port 25e is driven in the closing direction. On the other
hand, when the movable cam piston strokes in the clutch connecting
direction, the flow port 25e is driven in the opening direction.
Moreover, when the movable cam piston strokes from a completely
released state in the clutch connecting direction, the flow port
25e will be gradually opened. In addition, when the electronically
controlled coupling 16 is in a released state immediately before
connection, the flow port 25e is at a maximum open state, and the
maximum open state of the flow port 25e will be maintained as long
as the electronically controlled coupling 16 is connected.
The oil passage 25f is a communication passage which constantly
communicates the clutch chamber 25b and the oil chamber 25c by
bypassing the partition wall 25a. The lubricating oil that has
accumulated in the clutch chamber 25b is introduced in this oil
passage 25f due to the centrifugal force accompanying the rotation
of the electronically controlled coupling 16. The oil passage 25f
is inclined to the oil chamber 25c side, so that the introduced
lubricating oil is adapted to flow into the oil chamber 25c.
Note that the clutch input shaft 16b penetrates the coupling case
25 and is inserted into the clutch chamber 25b. The clutch output
shaft 16d penetrates the coupling casing 25 and the partition wall
25a, and is inserted into the clutch chamber 25b through the oil
chamber 25c. Further, in FIG. 1, an oil seal is denoted by a
reference numeral 25g, and a bearing is denoted by a reference
numeral 25h. The oil seals 25g, while preventing the lubricating
oil from leaking from the coupling case 25, rotatably supports the
clutch input shaft 16b and the clutch output shaft 16d. The bearing
25h allows circulation of the lubricating oil. The lubricating oil
reserved in the oil chamber 25c is allowed to leak in the clutch
chamber 25b through the bearing 25h in a small amount even when the
flow port 25e is closed by the on-off valve 25d.
Control System for a Four-Wheel Drive Vehicle
FIG. 2 schematically illustrates a control system for a four-wheel
drive vehicle of a front wheel drive base to which a clutch control
device is applied. Below, with reference to FIG. 2, description is
given of the control system of the four-wheel drive vehicle.
The four-wheel drive vehicle control system, as shown in FIG. 2,
includes an engine control module 31 (denoted as "ECM" in FIG. 2),
a transmission control module 32 (denoted as "TCM" in FIG. 2), an
ABS actuator control unit 33 (denoted as "ABS actuator C/U" in FIG.
2), and a 4WD control unit 34 (denoted as "4WD C/U" in FIG. 2).
The engine control module 31 is a control device of the transverse
engine 1 and receives detection signals from an engine speed sensor
35, an accelerator opening sensor 36, and the like. Through this
engine control module 31, the 4WD control unit 34 receives, via the
CAN communication line 37, the engine speed information and the
accelerator opening information (ACC information).
The transmission control module 32 is a control device of the
transmission 2, and receives detection signals from a transmission
input speed sensor 38, a transmission output speed sensor 39 and
the like. Through this transmission control module 32, the 4WD
control unit 34 receives, via the CAN communication line 37, the
gear ration information (speed ratio information).
The ABS actuator control unit 33 is a control device of the ABS
actuator (not shown) for controlling the brake fluid pressure of
each wheel, and receives detection signals from a yaw rate sensor
40, a lateral G sensor 41, a longitudinal G sensor 42, and wheel
speed sensors 43, 44, 45, 46, and the like. Through the ABS
actuator control unit 33, the 4WD control unit 34 receives, via the
CAN communication line 37, the wheel speed information, the yaw
rate information, and the lateral G information, the longitudinal G
information, and wheel speed information of each wheel. Note that,
in addition to the above information, steering angle information
from the steering angle sensor 47 is input to the 4WD control unit
34 via the CAN communication line 37.
The 4WD control unit 34 is a control device for controlling the
connecting/releasing of the dog clutch 8 as well as the
electronically controlled coupling 16, and performs arithmetic
processing based on various input information. Also, the 4WD
control unit 34 outputs a drive control command to a dog clutch
actuator 48 (solenoid pin) and an electronically controlled
coupling actuator 49 (electric motor). Here, as the input sources
other than the CAN communication line 37, a drive mode selection
switch 50, a brake switch 51 for detecting the presence or absence
of brake operation, a ring gear rotation speed sensor 52, a dog
clutch stroke sensor 53, a motor rotational angle sensor 54 and the
like are provided.
The drive mode selection switch 50 is a switch operable by the
driver for selecting "2WD mode", "Lock mode" and "Auto mode". When
the "2WD mode" is selected, a 2WD state (2-wheel drive) is
maintained in which the front wheels are driven with the dog clutch
8 and the electronically controlled coupling 16 released. When the
"Lock mode" is selected, a full 4WD state (4-wheel drive) is
maintained with the dog clutch 8 and the electronically controlled
coupling 16 connected. Further, when the "Auto mode" is selected,
the drive mode is automatically switched by automatically
controlling connecting/releasing of the dog clutch 8 and the
electronically controlled coupling 16 in accordance with the
vehicle state (vehicle speed, accelerator opening).
Here, in the "auto mode", there is a choice of an "Eco-auto mode"
to be selected when focusing on improving fuel efficiency and a
"Sport-auto mode" to be selected when focusing on four-wheel-drive
performance. Depending on the choice selected, i.e. selection mode,
the state of the electronically controlled coupling 16 is different
in a stand-by two-wheel drive mode with the dog clutch 8 connected
and the electronically controlled coupling 16 released. More
specifically, at the time of selection of the "Eco-auto mode", in
the Standby two-wheel drive mode, the electronically controlled
coupling 16 is placed in a stand-by state in a completely released
state. At this time, the flow port 25e is closed by the on-off
valve 25d so that the lubricating oil is stored in the oil chamber
25c. In contrast, at the time of selection of the "Sport-auto
mode", in the standby two-wheel drive mode, the electronically
controlled coupling 16 is placed in the stand-by state with
electronically controlled coupling 16 in the released state
immediately before connection. At this time, the on-off valve 25d
opens the flow port 25e, and the lubricating oil flows into the
clutch chamber 25b. Note that the "Eco-auto mode" and "Sport-auto
mode" are subject to selection arbitrarily by the driver.
Further, the "completely released state" is referred to a state in
which the input side clutch plate 16a and the output side clutch
plate 16c of the electronically controlled coupling 16 are
separated from each other, and both plates 16a and 16c are
maintained free from any contact without generating a clutch
connecting capacity immediately after the stroke of the movable cam
piston in the clutch connecting side. In addition, the "released
state immediately before connection" is referred to a state in
which, although the clutch connecting capacity is zero, the input
side clutch plate 16a and the output side clutch plate 16c are in
contact slightly, and a slight stroke of the movable cam piston in
the clutch connecting direction would cause an immediate occurrence
of the clutch connecting capacity.
The ring gear rotation speed sensor 52 is intended to be a sensor
for acquiring the output speed information of the dog clutch 8, and
calculates the output rotation speed of the dog clutch 8 by
considering, in addition to the ring gear rotation speed detected
value, the rear side gear ratio and the front side gear ratio. The
input rotation speed information of the dog clutch 8 is obtained by
calculation using the engine speed, gear ratio, and the final gear
ratio.
Drive Mode Switching
FIG. 3 is a drive mode switching graph based on a vehicle speed and
an accelerator opening at the time of selection of "Auto mode".
FIG. 4 shows the switching transition of the drive modes
(disconnect two-wheel drive mode, standby two-wheel drive mode, and
connect four-wheel drive mode). Below, with reference to FIGS. 3
and 4, a description is given of the drive mode switching
configuration.
In the first embodiment, as the drive modes when the "Auto mode" is
selected, the disconnect two-wheel drive mode (Disconnect), standby
two-wheel drive mode (Stand-by), and connect four-wheel drive mode
(Connect) are available. Further, switching among the three drive
modes is made based on the drive mode switching map shown in FIG. 3
by the 4WD control unit 34 based on the vehicle speed (VSP) and the
accelerator opening (ACC) representative of the required driving
force of the driver. That is, the 4WD control unit 34 corresponds
to a drive mode switching unit for switching the drive mode to any
one of the three drive modes.
In accordance with the vehicle speed and the accelerator opening,
the drive mode switching map, as shown in FIG. 3, is configured to
be divided into the disconnect two-wheel drive mode (referred to as
"differential speed control region (Disconnect)" in FIG. 3),
standby two-wheel drive mode (referred to as "differential speed
control region (Stand-by)" in FIG. 3), and connect four-wheel drive
mode (referred to as "driving force distribution region (Connect)"
in FIG. 3), respectively. The three drive modes is divided by a
region dividing line A in which the accelerator opening is
increased in proportion to increase in the vehicle speed from a
base point "a" which set at a vehicle speed VSP0 (threshold vehicle
speed) with the accelerator opening zero and another region
dividing line B (threshold required driving force) defined by a
constant accelerator opening ACC0 starting from an intersection b
with the region dividing line A in a high vehicle speed
direction.
The disconnect two-wheel drive mode (differential rotation control
region (Disconnect)) is defined in a region surrounded by a vehicle
speed axis with the accelerator opening zero, the region dividing
line A, and the region dividing line B where the accelerator
opening is set at ACC0 or below. That is, the mode corresponds to
the region in which, since the accelerator opening is equal to or
below the predetermined opening ACC0 (driver requested driving
force is low) despite a high vehicle speed region, the differential
rotation between the left and right front wheels 6 and 7 and the
left and right rear wheels 19 and 20 occurs rarely due to the drive
slip. Further, even when the drive slip occurs, the increase is
slow and gentle, and thus the demand for four-wheel drive
performance is low.
The stand-by two-wheel drive mode (differential rotation control
region (Stand-by)) is defined in a region which exceeds the preset
accelerator opening ACC0, and is surrounded by the region dividing
line A and the region dividing line B. That is, the mode
corresponds to the region in which, since the accelerator opening
exceeds the preset opening ACC0 (driver requested driving force is
high), though low in the demand for four-wheel driving performance,
once the differential rotation occurs between the left and right
front wheels 6 and 7 and the left and right rear wheels 19 and 20,
it is highly likely that the slip increases rapidly.
The Connect four-wheel drive mode (driving force distribution
region (Connect A)) is defined in a region surrounded by a vehicle
speed axis with the accelerator opening being zero, the region
dividing line A, and the region dividing line B. In other words,
the mode corresponds to the region in which the demand for four
wheel performance is high at the time of vehicle start or high load
travel with a large accelerator opening with low vehicle speed (low
vehicle speed region).
Once the disconnect two-wheel drive mode is selected, as shown in a
frame line C in FIG. 4, "the "2WD travel (Disconnect) mode" is in
place in which the dog clutch 8 and electronically controlled
coupling 16 are both released. In the disconnect two-wheel drive
mode, two-wheel drive traveling by the front wheel drive
(hereinafter referred to as "2WD traveling") is maintained in which
the driving force is essentially transmitted only to the left and
right front wheels 6 and 7. However, when a drive slip occurs in
the left and right front wheels 6 and 7 during the 2WD traveling
and the amount of the drive slip (or drive slip ratio) is more than
a threshold, the electronically controlled coupling 16 is
frictionally connected. Subsequently, when a rotational
synchronization state is determined, the dog clutch 8 is in meshing
connection to transfer to a 4WD traveling (hereinafter referred to
as "4WD traveling"). Accordingly, the differential rotation control
to suppress the driving slip takes place by allocating the driving
force to the left and right rear wheels 19 and 20 as well.
When the stand-by two-wheel drive mode is selected, as shown in the
frame line D in FIG. 4, the dog clutch 8 is connected and the
electronically controlled coupling 16 is released to introduce the
"2WD traveling (Stand-by)". In this stand-by two-wheel drive mode,
although the dog clutch 8 is meshed for connection, the driving
force is essentially transmitted only to the left and right front
wheels 6 and 7 to maintain the 2WD traveling of front wheel drive.
However, when a drive slip occurs in the left and right front
wheels 6 and 7 during the 2WD traveling of front wheel drive and
the amount of drive slip (or drive slip rate) exceeds a threshold,
since the dog clutch 8 is meshed in advance, only the frictional
coupling of the electronically controlled coupling 16 is performed.
Due to the frictional connection of the electronically controlled
coupling 16, by distributing the driving force to the left and
right rear wheels 19 and 20 with a good response, the differential
rotation control to suppress the driving slip may be performed.
When the Connect four-wheel drive mode is selected, as shown in a
frame line E in FIG. 4, the dog clutch 8 and electronically
controlled coupling 16 are both connected to reach the "4WD
traveling (Connect)". In this Connect 4WD mode, an optimal driving
force distribution control takes place in which the driving force
is optimally distributed between the left and right front wheels 6
and 7 and the left and right rear wheels 19 and 20 (distribution
control between front and rear wheels at the time of vehicle start,
for example) to suit the road conditions basically. However, during
the driving force distribution control, when a vehicle turning
state is determined based on the information from the steering
angle sensor 47, the yaw rate sensor 40, the lateral G sensor 41,
and longitudinal G sensor 42, control is performed to suppress the
tight corner braking phenomenon by reducing the connecting or
torque capacity the electronically controlled coupling 16.
A switching transition takes place among the disconnect two-wheel
drive mode (2WD traveling (Disconnect)), the stand-by two-wheel
drive mode (2WD traveling (Stand-by)), the connect 4WD drive mode
(4WD traveling (Connect)) in response to a switching request being
output when an operating point determined by the vehicle speed and
the accelerator opening crosses the regions dividing line A or the
region dividing line B shown in FIG. 3. With respect to the
switching transition speed to respective drive modes is set such
that the transition speed to the drive mode in response to 4WD
request is given priority over the transition speed to the
disconnect two-wheel drive mode to meet fuel economy
requirements.
More specifically, with respect to the switching transition speed
from the 2WD traveling (Disconnect) to 2WD traveling (Stand-by)
(arrow F in FIG. 4), the switching transition speed from the 2WD
traveling (Stand-by) to the 2WD traveling (arrow G in FIG. 4) is
set slower. Similarly, with respect to the switching transition
speed from the 2WD traveling (Disconnect) to the 4WD traveling
(Connect) (arrow H in FIG. 4), the switching transition speed from
the 4WD traveling (Connect) to the 2WD traveling (Disconnect)
(arrow I in FIG. 4) is made slower. On the other hand, the
switching transition speed from the 2WD traveling (Stand-by) to the
4WD traveling (Connect) (arrow J in FIG. 4) and the switching
transition speed from the 4WD traveling (Connect) to the 2WD
traveling (Stand-by) (arrow K in FIG. 4) is in the same speed.
Further, the "transition speed" is referred to the time for
transition completion after a switching request occurs. Here, when
the transition speed is slow (arrow G, arrows I), the mode
transition control starts after the elapse of a predetermined time
following a switching request output. In addition, when the
transition speed is fast (arrow F, the arrow H, arrow J, and arrow
K), the mode transition control starts immediately after the
switching request output.
Drive Mode Switching Process
FIG. 5 illustrates a flow of the drive mode switching process
executed by the 4WD control unit. Below, a description is given of
each step in FIG. 5 representing the drive mode switching process.
Note that the drive mode switching process is executed when the
"Auto mode" is selected by the drive mode selection switch 50.
In step S1, the current vehicle speed and the accelerator opening
are detected, and control proceeds to step S2. Here, the vehicle
speed is calculated from the wheel speeds of the left and right
rear wheels 19 and 20, which in turn are detected by the wheel
speed sensors 45 and 46, respectively. The accelerator opening is
detected by the accelerator opening sensor 36.
In step S2, following the detection of the vehicle speed and the
accelerator opening in step S1, based on the detected vehicle speed
and the accelerator opening and in accordance with the drive mode
switching map shown in FIG. 3, a drive mode is selected. Depending
on the drive mode thus selected, control proceeds to one of step
S3, step S4, and step S5. That is, when the vehicle speed is a
higher than the region dividing lines A, and the accelerator
opening is lower than the region dividing line B, the disconnect
two-wheel drive mode (2WD traveling (Disconnect)) is selected, and
control proceeds to step S3. Further, when the vehicle speed is a
higher than the region dividing lines A, and the accelerator
opening is larger than the region dividing line B, the stand-by
two-wheel drive mode (2WD traveling (Stand-by)) is selected, and
control proceeds to step S4. Still further, when the vehicle speed
is lower than the region dividing lines A, the Connect four-wheel
drive mode (4WD traveling (Connect)) is selected, and the process
moves on to step S5.
In step S3, following the selection of the disconnect two-wheel
drive mode in step S2, the disconnect two-wheel drive mode process
to be described below is executed, and control proceeds to
RETURN.
In step S4, following the selection of the standby two-wheel drive
mode in step S2, the stand-by two-wheel drive mode process to be
described below is executed, and control proceeds to RETURN.
In step S5, following the selection of the Connect four-wheel drive
mode in step S2, the Connect four-wheel drive mode process is
executed to be described below, and control goes to return.
The disconnect two-wheel drive mode process executed in step S3 has
the steps shown in FIG. 6. Below, a description is given of each
step of the disconnect two-wheel drive mode process.
In step S301, it is determined whether or not the electronically
controlled coupling 16 is in a released state. If YES (i.e.,
electronically controlled coupling is released), control proceeds
to step S303. If NO (electronically controlled coupling connected),
control proceeds to step S302. Here, the released state of the
electronically controlled coupling 16 is determined based on the
detected value of the motor rotation angle sensor 54.
In step S302, subsequent to the determination on the electronically
controlled coupling connection in step S301, a releasing command is
output to completely release the electronically controlled coupling
16, and control returns to step S301. Here, by outputting the
complete releasing command of the electronically controlled
coupling 16, the movable cam piston strokes in the releasing
direction in response to the electronically controlled coupling
actuator 49 to thereby bring the electronically controlled coupling
in a completely released state.
In step S303, following the determination of complete release of
the electronically controlled coupling in step S301, it is
determined whether or not the dog clutch 8 is in a released state.
If YES (dog clutch released), control proceeds to step S 305. In
the case of NO (dog clutch meshed), control proceeds to step S304.
Here, the released state of the dog clutch 8 is determined based on
the detected value of the dog clutch stroke sensor 53.
In step S304, following the determination of the dog clutch
connection in step S 303, a releasing command is output to release
the dog clutch 8, and control returns to step S303. Here, in
response to the output of the releasing command of the dog clutch
8, the solenoid pin and the movable member are fitted together by
the dog clutch actuator 48, and the movable member will rotate to
allow the movable member to stroke in the releasing direction to
thereby render the dog clutch 8 in a released state.
In step S305, subsequent to the determination on the dog clutch
release in step S303, both of the dog clutch 8 and the
electronically controlled coupling 16 is put in standby state in
the released states, the process goes to End. Note that, in this
disconnect two-wheel drive mode, when the drive slip in the left
and right front wheels 6 and 7 has occurred, the electronically
controlled coupling 16 and the dog clutch 8 are connected in order
to distribute the driving force to the left and right rear wheels
19 and 20 so that the differential rotation control is started to
suppress the driving slip. Then, when the drive slip settles out,
the electronically controlled coupling 16 and the dog clutch 8 are
released in sequence.
The stand-by two-wheel drive mode process executed in step S4
includes the steps shown in FIG. 7. Below, a description will be
given of each step of the standby two-wheel drive mode process.
In step S401, it is determined whether or not the "Eco-auto mode"
is selected. If YES (Eco-auto mode selected), control proceeds to
step S402. If NO (Sport-auto mode selected), control proceeds to
step S409. The selection determination of the "Eco-auto mode" is
made based on the selection result by the drive mode selection
switch 50.
In step S402, following the determination on the "Eco-Auto Mode"
selection in step S401, it is determined whether or not the
electronically controlled coupling 16 is in a released state. If
YES (electronically controlled coupling released), control proceeds
to step S403. If NO (electronically controlled coupling connected),
control proceeds to step S404.
In step S403, following the determination of the electronically
controlled coupling release in step S402 or the determination that
the rotational synchronization of the dog clutch 8 is NO in step
S405, a connection command to frictionally connect the
electronically controlled coupling 16 is output, and control
advances to step S404. Here, in response to the output of the
connection command of the electronically controlled coupling 16,
the movable cam piston is caused to stroke in the connecting
direction by the electronically controlled coupling actuator 49,
and the electronically controlled coupling 16 is connected.
In step S404, following the determination of the electronically
controlled coupling connection in step S402, or following the
output of the connection command of the electronically controlled
coupling 16 in step S403, it is determined whether or not the dog
clutch 8 is in a released state. If YES (dog clutch released),
control proceeds to step S405. In the case of NO (dog clutch
connected), control proceeds to step S407.
In step S405, following the determination of the dog clutch release
in step S404, it is determined whether or not the rotational
synchronization state of the dog clutch 8 is confirmed. If YES
(rotational synchronization OK), control proceeds to step S406. If
NO (rotational synchronization NG), control returns to step S403.
Here, by frictional connection of the electronically controlled
coupling 16, rotation of the left and right rear wheels 19 and 20
is transmitted to the bevel gear 9 via a propeller shaft 12, etc.,
and the output side meshing member of the dog clutch 8 that is
connected to the bevel gear 9 is rotated. Further, the input-side
meshing member of the dog clutch 8, which is connected to the
differential case of the front differential 3 is rotated by the
rotation of the left and right front wheels 6 and 7. The
determination of the rotational synchronization state is made by
confirming that the rotation speed difference between the
input-side meshing member of the dog clutch 8 connected to the
differential case of the front differential gear 3 and the output
side meshing member of the dog clutch 8 connected to the bevel gear
9 falls below a predetermined value.
In step S406, following the determination that the rotational
synchronization of the dog clutch 8 is OK in step S405, a
connection command for meshing connection of the dog clutch 8 is
output, and control proceeds to step S407. Here, the output of the
connection command of the dog clutch 8 allows the dog clutch
actuator 48 to release the fitting between the solenoid pin and the
movable member and to stroke the moving member in the connecting
direction by a spring bias to thereby connect the dog clutch 8.
In step S407, following the determination of the dog clutch
connection in step S404, or following the output of the connection
command of the dog clutch 8 in step S406, a releasing command will
be output to completely release the electronically controlled
coupling 16, and control proceeds to step S408.
In step S408, followed the output of the complete releasing command
of the electronically controlled coupling 16 in step S407, the dog
clutch 8 is put in a connected or meshed state and the
electronically controlled coupling 16 is put in a completely
released state, to thereby put in a stand-by state. Then, control
ends. Here, by putting the electronically controlled coupling 16 in
the complete released state, the on-off valve 25d closes the flow
port 25e, and the lubricating oil is stored in the oil chamber 25c.
Note that, in the stand-by two-wheel drive mode in the "Eco-Auto
mode", when the drive slip in the left and right front wheels 6 and
7 is generated, by connecting the electronically controlled
coupling 16 and distributing the driving force to the left and
right rear wheels 19 and 20, the difference rotation control to
reduce the drive slip is done. Then, when the drive slip is
converged, the electronically controlled coupling 16 is put in a
completely released state.
In step S409, following the determination of the "Sport-auto mode"
selection in step S401, it is determined whether or not the
electronically controlled coupling 16 is in a released state. If
YES (electronically controlled coupling released), control proceeds
to step S410. If NO (electronically controlled coupling connected),
control proceeds to step S411.
In step S410, following the determination of the electronically
controlled coupling release in step S409, or, following the
determination of the rotational synchronization of the dog clutch 8
being NG in step S412, a connection command for frictional
connection of the electronically controlled coupling 16 is output,
and control proceeds to step S411.
In step S411, following the determination of the electronically
controlled coupling connection in step S409, or, following the
output of the connection command of the electronically controlled
coupling 16 in step S410, it is determined whether or not the dog
clutch 8 is in a released state. If YES (dog clutch released),
control proceeds to step S412. In the case of NO (dog clutch
connected), control proceeds to step S414.
In step S412, following the determination of the dog clutch release
in step S 411, it is determined whether or not the rotational
synchronization state of the dog clutch 8 is confirmed. If YES
(rotational synchronization OK), control proceeds to step S413. If
NO (rotational synchronization NG), control returns to step
S410.
In step S413, after judging that the rotational synchronization OK
of the dog clutch 8 in step S412, and outputs the meshing command
to the fastening meshing of the dog clutch 8, the process proceeds
to step S414.
In step S414, following the determination of the dog clutch
connection or meshing in step S411, or, following the output of the
connection command of the dog clutch 8 in step S413, a releasing
command of the electronically controlled coupling 16 in the
released state immediately before connection, and control advances
to S415.
In step S415, following the output of the releasing command to the
released state of the electronically controlled coupling 16
immediately before connection in step S414, the dog clutch 8 is put
in a meshed state, the electronically controlled coupling 16 is
brought in a released state immediately before connection and
thereby set in a stand-by state. Subsequently, control goes to the
end. Here, by bringing the electronically controlled coupling 16 to
the state immediately before connection, the on-off valve 25d opens
the flow port 25e, and the lubricating oil flows into the clutch
chamber 25b. In this "Sport-auto mode" in the stand-by two-wheel
drive mode, when the drive slip in the left and right front wheels
6 and 7 is generated, a difference rotation control to reduce the
drive slip is done by connecting the electronically controlled
coupling 16 and distributing the driving force to the left and
right rear wheels 19 and 20. Then, the drive slip settles out, the
electronically controlled coupling 16 is released to produce a
released state immediately before connection.
The Connect four-wheel drive mode process executed in step S5 has
steps shown in FIG. 8. Below, a description will be given of each
step of the Connect four-wheel drive mode process.
In step S501, it is determined whether or not the electronically
controlled coupling 16 is in a released state. If YES
(electronically controlled coupling released), control proceeds to
step S502. If NO (electronically controlled coupling connected),
control proceeds to step S503.
In step S502, following the determination of the electronically
controlled coupling release in step S501, or following the
determination of the rotational synchronization of the dog clutch 8
being NG at step S504, a connection command to frictionally connect
the electronically controlled coupling 16 is output. Subsequently,
control proceeds to step S503.
In step S503, following the determination of the electronically
controlled coupling connection in step S501, or following the
output of the connection command of the electronically controlled
coupling 16 in step S502, it is determined whether or not the dog
clutch 8 is released. If YES (dog clutch released), control
proceeds to step S504. In the case of NO (dog clutch connected),
control proceeds to step S506.
In step S504, following the determination of the dog clutch release
in step S503, it is determined whether or not the rotational
synchronization state of the dog clutch 8 is confirmed. If YES
(rotational synchronization OK), control proceeds to step S505. If
NO (rotational synchronization NG), control returns to step
S502.
In step S505, following the determination that the rotational
synchronization of the dog clutch 8 is OK in step S504, a
connection command is output for meshing connection of the dog
clutch, and control proceeds to step S506.
In step S506, following the dog clutch connection in step S503, or,
following the output of the connection command of the dog clutch 8
in step S505, both of the dog clutch 8 and the electronically
controlled coupling 16 are put in a stand-by mode by putting both
in an connected state, and control moves on to end. Note that, in
this Connect four-wheel drive mode, by controlling the connecting
force of the electronically controlled coupling 16, with respect to
the left and right front wheels 6 and 7, and the left and right
rear wheels 19 and 20, the optimal driving force distribution
control for the driving force distribution is carried out tailored
to the road conditions and driving conditions.
Next, description will be given of the operation of the clutch
control device for a four-wheel drive vehicle of the first
embodiment, separately in the "drive mode switching operation", and
"switching timing setting operation of the drive mode".
Drive Mode Switching Operation
FIG. 9 is an explanatory flow diagram showing the movement of the
operating point on the drive mode switching map in the four-wheel
drive vehicle in the first embodiment. Below, with reference to
FIG. 9, a description is give of the drive mode switching operation
of the embodiment 1.
In the four-wheel drive vehicle in the first embodiment, when the
driver selects the "Auto mode", the drive mode switching process
shown in FIG. 5 is executed. Here, since the vehicle is stopped
before the vehicle starts, the vehicle speed is zero. In addition,
an accelerator opening is also zero because the accelerator is not
depressed. Therefore, as shown in FIG. 9, the operating point on
the drive mode switching map is positioned at point .alpha.
(alpha).
Then, when the accelerator pedal is depressed and the vehicle is
started, the operating point moves to the position of the point
.beta.. At this time, since both point .alpha. and point .beta. are
in the Connect four-wheel drive mode (driving force distribution
region (Connect)), in the flowchart shown in FIG. 5, control
proceeds from step S1, via step S2, to step S5, and the Connect
four-wheel drive mode process is performed. That is, at the time of
vehicle start, when the dog clutch 8 and the electronically
controlled coupling 16 are both connected, in the flowchart shown
in FIG. 8, control proceeds from step S501 to step S506 via S503,
and the dog clutch 8 and the electronically controlled coupling 16
are moth maintained in the connected state to perform the 4WD
traveling by distributing the driving force to the left and right
front wheels 6 and 7 to the left and right rear wheels 19 and
20.
Further, when the dog clutch 8 and the electronically controlled
coupling 16 are both released at the time of vehicle start, in the
flowchart shown in FIG. 8, control proceeds from step S501 to step
S502, and the electronically controlled coupling 16 is frictionally
coupled. Thus, the rotation of the left and right rear wheels 19
and 20 is transmitted from the left and right rear wheels drive
shafts 17, 18 through the electronically controlled coupling 16,
the rear differential 15, the ring gear 14, and the drive pinion
13, to the propeller shaft 12, to thereby rotate the propeller
shaft 12. Further, the distal end of the propeller shaft 12 is
connected to the output side meshing member through the output
pinion 10 and the bevel gear 9. Therefore, by frictional connection
of the electronically controlled coupling 16, the left and right
rear wheels 19, 20 are rotated to thereby rotate the output side
meshing member of the dog clutch 8.
On the other hand, the input-side meshing member of the dog clutch
8 is rotated by the front-wheel driving system, because the
input-side member is connected to the differential case of the
front differential 3. Further, as the connecting force of the
electronically controlled coupling 16 increases, the rotation speed
of the output-side meshing member of the dog clutch 8 increases.
When the dog clutch 8 is rotated in a synchronous state, control
proceeds from step S503 through step S504 to step S505, and the dog
clutch 8 is meshed.
Then, control proceeds to step S506 where both of the dog clutch 8
and the electronically controlled coupling 16 are maintained in the
connected state, and the 4WD traveling is carried out by
transmitting the driving force to the left and right front wheels
6, 7 and to the left and right rear wheels 19 and 20. In this
Connect four-wheel drive mode, by controlling the connecting force
of the electronically controlled coupling 16, an optimal driving
force distribution control to the driving force distribution is
carried out with respect to the left and right front wheels 6 and 7
and the left and right rear wheels 19 and 20, tailored to the road
conditions and driving conditions.
Then, such a case is assumed in which, as the vehicle speed is
gradually increased, and the operating point on the drive mode
switching map crosses the region dividing line A to move on the
position of point .gamma.. At this time, since the operating point
reaches in a higher vehicle speed region than the region dividing
line A, while maintaining the accelerator opening with a set
opening ACC0 or above, the system will move to the Standby
two-wheel drive mode (differential rotation control region
(Standby). That is, when the operating point crosses the region
dividing lines A, a switching request from the Connect four-wheel
drive mode to the Standby two-wheel drive mode is outputted.
Thus, in the flowchart shown in FIG. 5, control proceeds from step
S1 through step S2 to step S4, and the stand-by two-wheel drive
mode process is performed. More specifically, control proceeds to
step S401 in the flowchart shown in FIG. 7, and it is determined
whether or not "Eco-auto mode" is selected. If "Eco-auto mode" is
selected, control proceeds to step S402. Here, since the switching
request from the connect four-wheel drive mode to the standby
two-wheel drive mode is output, both the dog clutches 8 and the
electronically controlled coupling 16 have already been connected.
Thus, control proceeds from step S402 through step S404 to step
S407, to release the electronically controlled coupling 16.
Then, control proceeds to step S408, and the dog clutch 8 is put in
a connected state while the electronically controlled coupling 16
is put in a completely released state. Thus, of the rear wheel
drive system, the drive system downstream of the electronically
controlled coupling 16 is disconnected from the front wheel drive
system so that the 2WD traveling of front-wheel drive is carried
out by transmitting the driving force only to the left and right
front wheels 6 and 7.
Further, when the "Eco-auto mode" is selected, the electronically
controlled coupling 16 is put in stand-by in a completely released
state. Therefore, it is possible to reduce the friction loss in the
electronically controlled coupling 16 and improve the fuel
economy.
Moreover, in the first embodiment, when the electronically
controlled coupling 16 is in a completely released state, the flow
port 25e is closed by the on-off valve 25d, and the lubricating oil
is stored in the oil chamber 25c. For this reason, it is possible
to reduce the lubrication oil amount between the input side clutch
plate 16a and the output side clutch plate 16c of the
electronically controlled coupling 16. As a result, in the
electronically controlled coupling 16, it is possible to suppress
the occurrence of oil drag torque and to further improve the fuel
efficiency by reducing the friction loss.
Also, in this stand-by two-wheel drive mode, when the drive slip in
the left and right front wheels 6 and 7 occurs, only the
electronically controlled coupling 16 is connected to distribute
the driving force to the left and right rear wheels 19 and 20, and
a difference rotation control will be carried out to suppress the
drive slip. Then, when the drive slip converges, the electronically
controlled coupling 16 will be released completely.
Thus, in the standby two-wheel drive mode, when the drive slip
occurs, it is possible to switch promptly from 2WD traveling to 4WD
traveling by frictionally connecting the electronically controlled
coupling 16 only, i.e., without waiting for meshing of the dog
clutch 8. Therefore, it is possible to allocate the driving force
to the left and right rear wheels 19 and 20 quickly and in good
response so that the drive slip may converge in a short time. In
particular, in the stand-by two-wheel drive mode, although the
system is set in a region in which the drive slip is highly likely
to increase rapidly, it is possible for the drive slip to converge
quickly.
Further, in the case of "Sport-auto mode" being selected, control
proceeds from step S401 to step S409. Here, since the dog clutch 8
and the electronically controlled coupling 16 are both connected
already, control proceeds from step S409 through step S411 to step
S414, to release the electronically controlled coupling 16. Then,
control proceeds to step S415, and the dog clutch is placed in a
connected state while the electronically controlled coupling 16 is
place in a released state immediately before connection.
Accordingly, upon occurrence of the drive slip, when the movable
cam piston of the electronically controlled coupling 16 strokes
even slightly in the clutch connecting side, the driving force
transmission takes place immediately to thereby allow to shift 2WD
traveling to 4WD traveling quickly. This makes it possible to
further distribute the driving force to the left and right rear
wheels 19 and 20 in good response so as to meet the four-wheel
drive performance requirements.
Further, in the present first embodiment, when the electronically
controlled coupling 16 is in a released state immediately before
connecting, the flow port 25e is opened by the on/off valve 25d,
and the lubricating oil flows into the clutch chamber 25b.
Therefore, it is possible to suppress the heat generation of the
electronically controlled coupling 16 to thereby protect the
clutch.
Then, a case is assumed where the accelerator pedal is released in
the preparation of vehicle stop. At this time, since the
accelerator opening becomes zero by releasing a foot from the
accelerator pedal, the operating point on the drive mode switching
map is moved from the position of the point .gamma. to the position
of point .delta.. However, since the vehicle speed is not reduced
immediately, although the accelerator opening is less than the set
opening ACC0, but the vehicle speed maintains the high vehicle
speed range greater than the region dividing line A. In other
words, the operating point is moved to the disconnect two-wheel
drive mode (differential rotation control region (Disconnect)).
Thus, when the operating point crosses the region dividing line B,
a switching request from the standby two-wheel drive mode to the
disconnect two-wheel drive mode is outputted.
Thus, in the flowchart shown in FIG. 5, control proceeds from step
S1 via step S2 to step S3, and the disconnect drive mode process is
performed. Here, since the switching request from the standby
two-wheel drive mode to the disconnect two-wheel drive mode is
output, only the dog clutch 8 is connected. Therefore, in the
flowchart shown in FIG. 6, control proceeds from step S301 via step
S303 and step S304 to step S305, and, the dog clutch 8 is released.
Thus, since both the dog clutch 8 and the electronically controlled
coupling 16 are set in a released state, 2WD traveling of the front
wheel drive is carried out by transmitting the driving force only
to the left and right front wheels 6, 7. At this time, because the
electronically controlled coupling 16 is already released, it is
sufficient to release only the dog clutch 8 for a rapid mode
transition. Further, in the disconnect two-wheel drive mode, when
the drive slip occurs in the left and right front wheels 6 and 7,
the electronically controlled coupling 16 is frictionally
connected, and the dog clutch 8 is put in a meshed connection after
rotational synchronization so that a differential rotation control
will be performed to suppress the drive slip by allocating the
driving force to the left and right rear wheels. Then, when the
drive slip converges, the dog clutch 8 and the electronically
controlled coupling 16 will be set in a released state again.
In the disconnect two-wheel drive mode, since the dog clutch 8 is
disengaged, the rotation of drive system downstream of the dog
clutch 8 (rotation such as the propeller shaft 12) is stopped. That
is, it is possible to separate the entire rear-wheel drive system
from the front wheel drive system, so that it is possible to
suppress friction loss and oil agitation loss to thereby improve
fuel consumption.
Then, when the vehicle speed is reduced, and the vehicle speed is
below the set vehicle speed VSP0, the operating point crosses the
region dividing line A, and moves to the Connect four-wheel drive
mode (driving force distribution area (Connect)). Thus, a switching
request from the disconnect two-wheel drive mode to the Connect
four-wheel drive mode is outputted.
Thus, in the flowchart shown in FIG. 5, control proceeds from step
S1 via step S2 to step S5 again, and the Connect four-wheel drive
mode process is performed. At this time, since the dog clutch 8 and
the electronically controlled coupling 16 are both released, in the
flowchart shown in FIG. 8, control proceeds from step S501 through
step S502, step S503, step S504, step S505 to step S506, and the
electronically controlled the coupling 16 is first frictionally
connected and the dog clutch 8 is meshed for 4WD traveling.
Note that in the case of running on a downward slope at the low
vehicle speed with a low accelerator opening, even with the
accelerator opening left small, the vehicle speed increases. In
other words, while the accelerator opening is below the set opening
ACC0, the operating point is moved to a high vehicle speed region
larger than the region dividing line A. For this reason, the
operating point on the drive mode switching map moves from the
point .alpha.1 in the Connect four-wheel drive mode (driving force
distribution area (Connect)), to a point .beta.1 in the disconnect
two-wheel drive mode (differential rotation control region
(Disconnect)), and a switching request from the Connect four-wheel
drive mode to the disconnect two-wheel drive mode is outputted.
At this time, since the dog clutch 8 and the electronically
controlled coupling 16 are both connected, in the flowchart shown
in FIG. 6, control proceeds from step S301 through step S302, step
S303, and step S304 to step S305, and the electronically controlled
coupling 16 is released with the dog clutch being subsequently
released so that both the dog clutch 8 and the electronically
controlled coupling 16 are in a released state.
Further, when traveling an uphill at high speed with large
accelerator opening, the vehicle speed decreases with a constant
accelerator position. In other words, while the accelerator opening
is held above the set opening ACC0, the operating point is moved to
a low vehicle speed region lower than the region dividing line A.
Thus, the operating point on the drive mode switching map is moves
from the point .alpha.2 in the standby two-wheel drive mode
(differential rotation control region (Stand-by)) to .beta.2 in the
Connect four-wheel drive mode (driving force distribution region
(Connect)), so that a switching request from the standby two-wheel
drive mode to the Connect four-wheel drive mode is outputted.
In this case, because the dog clutch 8 is already is connected, in
the flow chart shown in FIG. 8, control proceeds from step S501 via
steps S502 and S503 to step S506, and only the electronically
controlled coupling 16 is connected to render both the dog clutch 8
and the electronically controlled coupling 16 in the engaged or
connected state. Thus, it is possible to switch quickly from 2WD
traveling to the 4WD traveling without waiting for meshing of the
dog clutch 8.
Furthermore, in the case of increased depression of the accelerator
pedal is performed during traveling at high speed with a low
accelerator opening, the accelerator opening is increased while
maintaining high speed. In other words, while the vehicle speed is
maintained at a high vehicle speed range larger than the region
dividing line A, the accelerator opening exceeds the region
dividing line B. Thus, the operating point on the drive mode
switching map is moved from the point .alpha.3 in the disconnect
two-wheel drive mode (differential rotation control region
(Disconnect)) to .beta.3 in the standby two-wheel drive mode
(differential rotation control region (Stand-by)) so that a
switching request from the disconnect two-wheel drive mode to the
standby two-wheel drive mode is outputted.
At this time, since the dog clutch 8 and the electronically
controlled coupling 16 have been both released, when, for example,
the Eco-auto mode is selected, in the flowchart shown in FIG. 7,
control proceeds from step S401 through step S402, step S403, step
S404, step S405, step S406, and step S407 to step S408. In other
words, in order to rotate the dog clutch 8 in synchronization, the
electronically controlled coupling 16 is temporarily connected.
After the rotational synchronization, when the dog clutch 8 is
connected, by releasing the electronically controlled coupling 16,
the dog clutch 8 is placed in a connected state while the
electronically controlled the coupling 16 is brought to a released
state.
Timing Setting Operation of Drive Mode Switch
In the clutch control device in the first embodiment, when "Auto
mode" is selected, based on the vehicle speed (VSP), the
accelerator opening representing the required driving force of the
driver (ACC), and the drive mode switching map shown in FIG. 3,
switching takes place among three modes of the disconnect two-wheel
drive mode (Disconnect), standby two-wheel drive mode (Stand-by),
and connect four-wheel drive mode (Connect), the three drive
mode.
At this time, as shown in FIG. 4, the transition speed when
switching from the standby two-wheel drive mode (2WD traveling
(Standby)) or from the Connect four-wheel drive mode (4WD traveling
(Connect)) to the disconnect two-wheel drive mode (2WD traveling
(Disconnect)) is set relatively slower. Also, when switching from
disconnect two-wheel drive mode (2WD traveling (Disconnect)) to the
standby two-wheel drive mode (2WD traveling (Standby)) or from
disconnect two-wheel drive mode (2WD traveling (Disconnect)) to the
connect four-wheel drive mode (4WD traveling (Connect)), and
further mutually between the stand-by two-wheel drive mode (2WD
traveling (Standby)) and the connect four-wheel drive mode (4WD
traveling (Connect)), the transition speed is set relatively
faster.
Therefore, when releasing the dog clutch 8 from meshing, or when
connecting the dog clutch 8 from releasing, a mode transition takes
place in a time delay from the output of the switching request.
Accordingly, when the operating point on the drive mode switching
map is not stable, it is possible to prevent connecting/releasing
of the dog clutch 8 from occurring so that the occurrence of
control hunting can be prevented.
Furthermore, in the first embodiment, the dog clutch 8 is disposed
upstream of the bevel gear 9 provided in the drive branch position
to the left and right front wheels 6 and 7 and the output pinion
10. Further, the electronically controlled coupling 16 is
configured to be disposed in the left rear wheel drive shaft 17
after the drive torque passes from the bevel gear 9 and the output
pinion 10 through the rear wheel output shaft 11, the propeller
shaft 12, the drive pinion 13, the ring gear 14, and the rear
differential 15. With this configuration, when the "disconnect
two-wheel drive mode" is selected, the bevel gear 9, the output
pinion 10, the rear wheel output shaft 11, the propeller shaft 12,
the drive pinion 13, ring gear 14, and the differential case of the
rear differential 15 is stopped to rotate. Therefore, when the
"disconnect two-wheel drive mode" is selected, the rotation of the
drive system extending from the dog clutch 8 to the to the
electronically controlled coupling 16 is rendered to be stopped so
that such as friction loss and oil agitation loss is effectively
suppressed to thereby achieve improved fuel efficiency.
Now, a description will be given of effects. In a clutch control
device for a four-wheel drive vehicle in the first embodiment, it
is possible to obtain the following effects.
(1) In a clutch control device for a four-wheel drive vehicle in
which one of the left and right front wheels and the left and right
rear wheels are set as main drive wheels that are connected to a
driving source (transverse engine 1), while the others are set as
auxiliary drive wheels that are connected to the driving source
(transverse engine 1) via a clutch, the clutch control device
performs selective connecting/releasing control of the clutch and
comprises a drive mode switching unit (4WD control unit) configured
to perform a switching control of the drive mode of the four-wheel
drive vehicle in accordance with a vehicle state, the clutch
including a meshing clutch (dog clutch 8) and a friction clutch
(electronically controlled coupling 16) disposed separately in the
driving force transmission system to the auxiliary drive wheels
(left and rear wheels) in a transmission path on the drive branch
side and in a transmission path on the auxiliary drive wheel side
with a differential interposed. The meshing clutch (dog clutch 8)
is configured to release the driving force transmission system
(rear driving system) to the auxiliary drive wheels (left and right
rear wheels 19 and 20) from the driving force transmission system
(front driving system) to the main drive wheels (left and right
front wheels 6 and 7). The friction clutch (electronically
controlled coupling 16) allocates part of a driving force from the
driving source (transverse engine 1) to the auxiliary drive wheels
(left and right rear wheels 19 and 20) in response to the clutch
connection capacity. The drive mode switching unit (4WD control
unit 34) is configured to switch the drive mode among one of a
disconnect two-wheel drive mode to release the meshing clutch (dog
clutch 8) and the friction clutch (electronically control coupling
16), a connect four-wheel drive mode to connect the meshing clutch
(dog clutch 8) and the friction clutch (electronically control
coupling 16), and a stand-by two-wheel drive mode to connect the
meshing clutch (dog clutch 8) and release the friction clutch
(electronically control coupling 16) Thus, it is possible to
perform switching from the two-wheel drive traveling (2WD
traveling) to the 4-wheel drive traveling (4WD traveling)
promptly.
(2) The drive mode switching unit (4WD control unit 34) is
configured, when focusing on improving fuel consumption in the
standby two-wheel drive mode, to bring the friction clutch
(electronically controlled coupling 16) in a completely released
state, and when focusing on the four-wheel drive performance in the
stand-by two-wheel drive mode, to bring the friction clutch
(electronically controlled coupling 16) in a released state
immediately before connection. Thus, in addition to the effect of
(1), during the stand-by two-wheel drive mode, when focusing on the
fuel efficiency, it is possible to achieve further improvement in
fuel consumption by preventing the occurrence of dragging torque in
the friction clutch (electronically controlled coupling 16).
Further, when focusing on the four-wheel drive performance, by
striving to shorten the connecting time of the friction clutch
(electronically controlled coupling 16) and switching more promptly
to the 4-wheel drive traveling (4WD traveling) from the 2-wheel
drive traveling (2WD traveling), it is possible to meet the demand
for four-wheel drive performance.
(3) The friction clutch (electronically controlled coupling 16) is
housed in a clutch case (coupling case 25). The clutch case
(coupling case 25) has a clutch chamber 25b housing the friction
clutch (electronically controlled coupling 16), an oil chamber 25c
defined from the clutch chamber 25b through a partition wall 25a,
an oil passage 25f communicating the clutch chamber 25b and the oil
chamber 25c for flowing lubricating oil from the clutch chamber 25b
into the oil chamber 25c due to a centrifugal force generated in
response to rotation of the friction clutch (electronically
controlled coupling 16), and an on-off valve 25d disposed in the
partition wall 25a. Further, the drive mode switching unit (4WD
control unit 34) is configured, when emphasizing fuel efficiency in
the stand-by two-wheel drive mode, to store the lubricating oil in
the oil chamber 25c by closing the on-off valve 25d, while, when
emphasizing the four-wheel drive performance in the stand-by
two-wheel drive mode, to allow the lubricating oil to flow from the
oil chamber 25c into the clutch chamber 25b by opening the on-off
valve 25d. Thus, in addition to the effect of (2), when emphasizing
fuel efficiency, it is possible to prevent the lubricating oil from
generating agitation resistance to thereby achieve further fuel
efficiency. Also, when emphasizing the four-wheel drive
performance, it is possible to supply the lubricating oil to the
friction clutch (electronically controlled coupling 16), to
suppress the heat generation of the friction clutch (electronically
controlled coupling 16), and to protect the clutch.
(4) The drive mode switching unit (4WD control unit 34) is further
configured, when the vehicle speed is higher than a predetermined
threshold vehicle speed and the required driving force of the
driver is lower than a predetermined threshold required driving
force, to switch the drive mode to the disconnect two-wheel drive
mode, when the vehicle speed is higher than the predetermined
threshold vehicle speed and the required driving force of the
driver is higher than the predetermined threshold required driving
force, to switch the drive mode to the standby two-wheel drive
mode, and when the vehicle speed is lower than the threshold speed,
switching the drive mode to the connect four-wheel drive mode.
Thus, in addition to the effect of any one of the above (1) to (3),
if there is a high possibility that the drive slip increases
rapidly at a high vehicle speed with a high accelerator opening,
the stand-by two-wheel drive mode is set to thereby allowing from
the two-wheel traveling (2WD traveling) to the 4-wheel traveling
(4WD traveling) to switch immediately. In addition, in the case of
a high-speed with a low-accelerator opening with a low level of
request for a four-wheel drive where a drive slip is increases
slowly, the disconnect drive mode is set to thereby stop the drive
system rotation on the downstream side from the meshing clutch (dog
clutch 8). Thus, it is possible to suppress friction loss and oil
agitation loss, to thereby achieve improved fuel efficiency.
(5) The drive mode switching unit (4WD control unit 34) is further
configured to give priority to a switching transition speed to the
stand-by two-wheel drive mode and switching transition speed to the
connect four-wheel drive mode over a transition speed to the
disconnect two-wheel drive mode. Thus, in addition to the effect of
any one of the above (1) through (4), when the position of the
operating point on the drive mode switching map is unstable, it is
possible to prevent performing meshing/releasing control of the
clutch (dog clutch 8) to thereby prevent the occurrence of control
hunting.
(6) The dog clutch (dog clutch 8) is disposed in the upstream
position of a transfer mechanism (bevel gear 9, output pinion 10)
provided in a drive branch position to the auxiliary drive wheels
(left and right rear wheels 19, 20). The friction clutch
(electronically controlled coupling 16) is disposed in a position
of the drive shaft (left rear drive shaft 17) leading to the
auxiliary drive wheel (rear left wheel 19) from the transfer
mechanism (bevel gear 9, output pinion 10) via a propeller shaft 12
and a differential (rear differential 15). Thus, in addition to the
effect of any one of the above (1) through (5), in front-wheel
drive-based a four-wheel drive vehicle, when the "disconnect
two-wheel drive mode" is selected, the friction loss and oil
agitation loss and the like are effectively suppressed to achieve
improved fuel efficiency.
The Second Embodiment
The second embodiment is an example in which the clutch control
device is applied to a four-wheel drive vehicle of the rear wheel
drive base and the arrangement of the meshing clutch and the
friction clutch with a differential interposed is in a reversed
relationship from the first embodiment.
FIG. 10 schematically illustrates a driving system of a four-wheel
drive vehicle with a rear-wheel drive base to which a clutch
control device is applied in accordance with a second embodiment.
Below, with reference to FIG. 10, a description is given of the
drive system configuration of the four-wheel drive vehicle.
As shown in FIG. 10, the rear wheel drive system of the four wheel
drive vehicle includes a longitudinal engine 61 (driving source), a
transmission 62, a rear propeller shaft 63, a rear differential 64,
a left rear wheel drive shaft 65, a right rear wheel drive shaft
66, a left rear wheel 67 (main drive wheel), and a right rear wheel
68 (main drive wheel). That is, the driving force passing through
the longitudinal engine 61 and the transmission 62 is transmitted
to the left and right rear wheels drive shafts 65 and 66 through
the rear propeller shaft 63 and the rear differential 64, to drive
the left and right rear wheels 67 and 68 at all times while
permitting a rotation difference.
As shown in FIG. 10, in the front wheel drive system of the
four-wheel drive vehicle, a transfer mechanism is configured such
that, in the transfer case 69, an electronically controlled
coupling 70 (friction clutch), an input sprocket 71, an output
sprocket 72, a chain 73 are provided. In addition, a front
propeller shaft 74 which is connected to the output sprocket 72, a
front differential 75, a left front wheel drive shaft 76, a right
front wheel drive shaft 77, a left front wheel 78 (auxiliary drive
wheel), and a right front wheel 79 (auxiliary drive wheel). The
electronically controlled coupling 70 is disposed inside the
transfer case 69 and positioned upstream of the input sprocket 71
(main drive system side position).
The dog clutch 80 (meshing clutch) is disposed in the intermediate
position of the left front wheel drive shaft 76 that connects the
front differential 75 and the left front wheel 78. That is, such a
two-wheel drive mode driving system is configured that is capable
of selecting a two-wheel drive mode (=disconnect two-wheel drive
mode) for releasing both the electronically controlled coupling 70
and the dog clutch 80. By releasing the electronically controlled
coupling 70 and the dog clutch 80, the drive system downstream of
the electronically controlled coupling 70 (rotation, such as the
front propeller shaft 74) is stopped to rotate is stopped to
suppress friction loss and oil agitation loss, etc. suppressed, so
that fuel efficiency is improved.
Now, a description is given of the synchronous operation of the dog
clutch 80. In the first embodiment, such a configuration is adopted
in which, in the driving force transmission system to the left and
right rear wheels 19 and 20 representing auxiliary drive wheels,
with a rear differential 15 interposed, in the driving force
transmission path on the driving force branch side, a dog clutch 8
is disposed, while, in a transmission path on the side of the
auxiliary drive wheel, an electronically controlled disposed
separately from each other. Therefore, at the time of a meshing
request for the dog clutch 8 in the released state, when the
meshing control of the electronically controlled coupling 16 is
done, the left side gear of the rear differential 15 is restricted
by the rotation speed of the left rear wheel 19. Therefore, of the
three rotary members (left and right side gears and the
differential case) of the rear differential 15, due to the rotation
speed of the left and right side gears being restricted, the
rotation speed of the propeller shaft 12 which is connected to the
differential case reaches the average of left and right rear wheels
19 (driven wheel rotation speed). As a result, when the left and
right front wheels 6 and 7 are in the non-slip state, the clutch
differential rotation .DELTA.N of the dog clutch 8 is zero
(.DELTA.N=0). However, when the left and right front wheels 6 and 7
are in a slip state, the clutch differential rotation .DELTA.N,
which are on decrease with the passage of time, become critical
when reaching a certain differential rotation. Subsequently, the
clutch rotation difference .DELTA.N changes to increase, along the
passage of time, the clutch differential rotation .DELTA.N will
increase.
In contrast, in the second embodiment, in the driving force
transmission system to the left and right front wheels 78 and 79
representing auxiliary drive wheels, it is configured such that,
with the front differential 75 interposed, an electronically
controlled coupling 70 is disposed in the transmission path on the
drive branch side, while a dog clutch 80 is disposed separately in
the transmission path on the side of auxiliary drive side,
respectively. Therefore, at the time of a meshing request for the
dog clutch 80 in the released state, when the meshing control of
the electronically controlled coupling 70 is done, the differential
case of the front differential 75 is restricted by the rotation
speed of the rear propeller shaft 63. Therefore, of the three
rotary members of the front differential 75 (left and right side
gears and the differential case), due to the rotation speed of the
differential case and right side gear (right front wheel 79) being
constrained, the rotation speed of the left side gear will be
determined by two rotational speeds. As a result, when the left and
right rear wheels 67 and 68 are in the non-slip state, the clutch
differential rotation .DELTA.N of the dog clutch 80 is zero
(.DELTA.N=0). However, when the left and right rear wheels 67 and
68 are in a slip condition, the clutch differential rotation
.DELTA.N decreases along with the passage of time, and would be
reversed after crossing a point of .DELTA.N being zero.
Subsequently, the clutch differential rotation .DELTA.N will
increase in the inverted state. Since other operations are the same
as in the first embodiment, the description thereof is omitted.
Now, a description will be given of effects. In the clutch control
device for a four-wheel drive vehicle in the second embodiment, the
following effect may be obtained.
(7) The friction clutch (electronically controlled coupling 70) is
disposed in the upstream position of a transfer mechanism (input
side sprocket 71, output side sprocket 72, and a chain 73) provided
at a drive branch position leading to the auxiliary drive wheels
(left and right front wheels 78 and 79). The meshing clutch (dog
clutch 80) is disposed in a drive shaft (left front wheel drive
shaft 76) leading to the auxiliary drive wheel (left front wheel
78) from the transfer mechanism via a propeller shaft (front
propeller shaft 74) and a differential (front differential 75).
Therefore, in addition to the effects of (1) to (5), in a
four-wheel drive vehicle of the rear wheel drive base, when the
"disconnect two-wheel drive mode" is selected, friction loss, oil
agitation loss and the like may be effectively suppressed. Thus, it
is possible to achieve improved fuel efficiency.
Although the clutch control device for a four-wheel drive vehicle
according to the present invention has been described based on the
first and second embodiments. The specific configuration is not
limited to these embodiments. Rather, changes in design, additions,
and the like are acceptable without departing from the gist of the
invention according to each claim,
For example, in the first embodiment, the dog clutch 8 is disposed
in a drive branch position to the left and right rear wheels 19 and
20 representing auxiliary drive wheels, whilst the electronically
controlled coupling 16 is disposed in the left rear wheel drive
shaft 17 downstream of the bevel gear 9, propeller shaft 12, and
the rear differential 15. However, the configuration is not limited
thereto. For example, the dog clutch 8 may be arranged between the
bevel gear 9 and the propeller shaft 12. Further, the
electronically controlled coupling 16 may be disposed at the
position in the right rear wheel drive shaft 18. Moreover, the
electronically controlled coupling may be disposed between the
propeller shaft 12 and the rear differential 15.
Furthermore, the dog clutch 8 may be constituted by a meshing
clutch which is subject to releasing/connecting by a shift fork
driven by hydraulic pressure. In addition, the electronically
controlled coupling 16 may be constituted by a hydraulic friction
clutch to release/connect a multi-plate clutch by hydraulic
pressure.
In the first embodiment, the clutch control device in a four-wheel
drive vehicle (4WD engine vehicle) is applied to a four-wheel drive
vehicle of front wheel drive equipped with an engine as driving
source. Also, in the second embodiment, the clutch control device
in a four-wheel drive vehicle (4WD engine vehicle) is applied to a
four-wheel drive vehicle of rear wheel drive in which main driving
source are left and right rear wheels. However, the invention may
be applied to a four-wheel drive vehicle of rear wheel drive base
in which the relative arrangement of the meshing clutch and the
friction clutch matches the relationship described in the first
embodiment. Further, the invention may be applied to a four-wheel
drive vehicle of front wheel drive base in which the relative
arrangement of the meshing clutch and the friction clutch matches
the relationship described in the second embodiment. Besides, the
invention may be applied, in addition to a 4WD engine vehicle, to a
4WD hybrid vehicle having a motor and an engine as driving source,
or a 4WD electric vehicle having a motor only as driving
source.
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